Apparatus for hardening metals



INVENTOR:

FIG. 3.

May 2, 1933.

FIG.

FRANK A. MILLIFF ATTORNEY.

y 2, 1933- F. A. MILLIFF 1,907,331

APPARATUS FOR HARDENING METALS Filed April 6, 1931 2 Sheets-Sheet 2 IN TOR:

FRANK A. MILLI ATTORNEY Patented May 2, 1933 PATENT. OFFICE FRANK A. mmrrr, or nos ANGELES, CALIFORNIA APPARATUS FOR HARDENING METALS Application filed April 6,- 1931. Serial No. 527,894.

This invention relates to improvements in' apparatus for hardening metals.

The principal object of the invention is to,

case harden fabricated metals such as ferrous alloys, v

Another object is to regenerate and conserve the active gases incidental to the-practice of the invention.

Another object is to reduce the applied temperature and the time period in the practice of this art.

Another object is to so treat the metal and applied gas that the afiinity between them will be increased.

A further object is to standardize and control the depth of penetration and reaction in the hardened case.

Other objects and advantages will appear as the description progresses.

Broadly stated, the invention consists in means for heating. the metal in evacuated receptacles and: introducing nascent nitrogen or other active chemicals to the, receptacle 1 at pressure below atmospheric. The boiling point of steel is lowered under vacuum and the nitriding of the case therefore can be accomplished at much lower tem- I peratures than are possible under plus pressures, as heretofore practiced.

The application of pressure below atmospheric decreases surface tension, grain growth and distortion and increases the available interstices by extracting the occluded gases. The cooling period is decreased about one-third, by excluding atmospherlc air from mace and p p to the for g g a check the box.

In this specification and the accompany-- ing drawings the invention is disclosed in its preferred form. It is to be understood, how-' ever, that it is not limited to this form because it may be embodied in other forms within the spirit of the claims following the description.

In the two sheets of drawings:

Fig. 1 is a diagrammatic front elevation of a hardening apparatus built in accordance with this invention.

r Fig. 2 is a horizontal section from above of the same on the line II-II, Fig. 1.

3 is an enlarged detail in vertical sec tion of a gas dissociator.

In detail the construction illustrated in the .drawings comprises the conventional muflie Such furfurnace, referring to Fig. 1. naces have the floor 1, side walls 2-3, top 4 and two ends 5-6. The whole interior is lined with refractory material and a suitable door 1 is provided for charging and discharging the furnace. The heat is applied to the interior of the furnace in any conventional manner such as the burner 1".

This method is equally applicable to electric furnaces surrounding the nitriding receptacle or box adapted to be evacuated or subjected to pressure below atmospheric.

In the present invention the average temperature for the treatment of steel and nitridable alloys is 900 to 1500 F. Thus far the equipment is in accord with common practice.

The closed treating boxes 7 are composed of steel or any suitable material not subject to or effected by the nascent gases used. The boxes are rendered vacuum-tight and must withstand the desired temperatures. They may be made to fill the space available within the furnace or in smaller units connected with intakes and outlets for the internal circulation of the desired gases through the boxes. The gas is introduced at the bottom of the box through the perforated pipe 8 and is withdrawn through the pipe 9 beneath the sealed cover 10. The box is provided with the vacuum gage 11, located outside the furon the conditions of vacuum within the box.

The pipe 9 leads outside the furnace to the ed to the vertical tube or. tower 20. Just beneath the apex the transverse bypass tube 21 is inserted between the tubes 1819 to which it is welded.

These tubes 1819 are filled with a suitable catalyst 22. Copper borings are preferred for anhydrous ammonia. The tower 20 is filled with coarse particles of unglazed porcelain 20 among which the separated hydrogen passes upward, as will be hereinafter more fully described.

The dissociator is preferably installed within the furnace and is subjected to the same temperature as the box 7 to facilitate the dissociation of the gases.

For nitriding steel and ferrous alloys the anhydrous ammonia in the tank 23, is carried through the valve 24 in the pipe 25 to the inlet 26 of the tube 18. The ammonia passing among the heated copper borings 22 begins a natural separation. The nitrogen being heavier settles out, while the lighter hydro gen rises in the tube 18. The nitrogen crosses through the bypass 21 to the tube 19 where the separation continues and the heavy nascent nitrogen passes out at the bottom of the tube 19 into the pipe 28. The lighter hydrogen from both tubes 1819 rises through a screen or perforations at the bottom of the tower 20 which impedes the possible rise of any associated nitrogen. Within the tower the separation is completed by the porcelain 20, and hydrogen escapes at the top of the tower through the pipe 29 and valve 30 to the top of the suction receiver 12. If the needle valve 30 is slightly opened a very low suction or pressure below atmospheric can be exerted on the top of the tower 20, just enough to withdraw the hydrogen without lifting the nitrogen over.

The hydrogen and other gases present in ammonia gas dilute the nitrogen and set up reactions impeding I the pentration of the nitrogen into the texture of the metal, rendered more porous by the applied heat.

The dissociator, Fig. 3. is under a slight pressure above atmospheric from the drum 23, up to the base of the tower 20. It is obvious that the dissociator eventually reduces the major constituent of the gas in the circulatory system to nascent nitrogen.

The interstices in the metal are gradually freed of occluded gases by the heat and re duced pressure within the box and said gases are replaced by the nascent nitrogen absorbed by the expanded metal and retained as the metal cools.

The nascent nitrogen may be separated from the ammonia gas in any other manner, for introduction into the reduced pressure Within the box 7. without departing from the spirit of this invention.

The outlet pipe 28 from the dissociator is led outside of the furnace and fitted with the stop valve 31 in the pipe 8 leading to the box 7. The valve 32 permits the attachment of a suitable pipette or suitable instrument through which the gas may be bypassed by means of the valve 32 for the purpose of analysis and check on the flow of nascent nitrogen from the dissociator.

It is Well to provide for the introduction of a thermo-couple 7 in the pipe 9 as shown or elsewhere for measuring the temperature of the interior of the box 7.

It has been the practice heretofore, so far as I am aware, to circulate the anhydrous ammonia gas through closed boxes, similar to 7, at atmospheric or plus pressure and depend upon the steel objects in the box to select the nitrogen from the combined gases until the nitrided case is formed on the objects. This method is wasteful of the gases, uncertain in ultimate eifect, with hit or miss results in the ultimate product.

There has been a further wasteful use of the valuable gases in passing them through the treating boxes to wash out atmospheric 7 air and occluded gases deleterious to the nitriding process, both before and after the application of heat. Such waste is eliminated in the present invention by the dissociator which very quickly reduces the major constituent of the ammonia gas to nascent nitrogen and maintains this condition during the period of operation. a

In the present instance only nitrogen in the active nascent state is fed to the box 7, which is absorbed by the porous surface of the objects in the box at reduced surface tension until the available interstices of the objects are completely filled by the molecules of nascent nitrogen, under constant check, without dilution and the deleterious reactions in-- cidental to the presence of excess hydrogen and any other gases that may be present in commercial anhydrous ammonia as heretofore used in nitriding steel.

This invention gives purified hydrogen as a valuable byproduct and stabilized nascent nitrogen applied in a manner to give the maximum nitriding effect on the metal with the utmost in conserving the applied gases. The hydrogen and excess nitrogen are recovered at the exhaust 16.

This invention is also applicable in carburizing steel by subjecting it to colloidal carbons under suitable conditions of temperature and pressure below atmospheric in the box 7. It is equally obvious that any heat treated object in the box 7 can be subjected to the absorption of any afiinity gases with improved results under the controlled conditions incidental to the practice of the spirit of this invention, by those skilled in the art.

Having thus described this invention what I claim and desire to cover by Letters Patent is:

1. A hardening apparatus including a heating furnace; a sealed box and a dissociator in said furnace; means for passing a gas through said dissociator and box at a. pressure below atmospheric.

2. A hardening apparatus including a heating furnace; a sealed box and dissociator in said furnace; means for passing ammonia gas through said dissociator and withdrawing hydrogen from said dissociator and passing the resulting nascent nitrogen through said box at a pressure below atmospheric.

3. A hardening apparatus including a heating furnace; a sealed box and dissociator in said furnace; means for circulating a nitriding gas through said dissociator and box at pressure below atmospheric and withdrawing hydrogen from said dissociator.

4. A hardening apparatus including a heating furnace; a sealed box and dissociator in said furnace; a receiver; a pump having its suction intake connected with said receiver; a circulatory system including said receiver; box and dissociator, and a gas supply connected with said dis'sociator:

5. A hardening apparatus including a gas dissociator having a catalyst therein and a separation tower thereon; a sealed box communicating with said dissociator; a source of ammonia gas communicating with said dissociator; a suction means connected with said box; and means for heating said box.

6. A hardening apparatus including -a dissociator having an arched tube containing a catalyst and connected with a separator at its high point; a source of ammonia gas discharging into said tube; a sealed box communicating with said tube; means for creating a suction on said box and tower and means for heating said box.

7. A hardening apparatus including a heating furnace; a dissociator; a sealed box in said furnace and connected with the lower portion of said dissociator; means for introducing a gas into said dissociator and means for withdrawing the gas from said box at a pressure below atmospheric.

8. A hardening apparatus including a furnace; a dissociator; a sealed box in said furnace connected with said dissociator; means for introducing a nitriding gas into said dissociator; and means for evacuating said box at a pressure below atmospheric.

In testimony whereof I have hereunto set my hand this 31st day of March, 1931.

FRANK A. MILLIFF. 

